1. Field of the Invention
The present invention relates to a TV system discriminator for automatically discriminating a TV (television) system corresponding to an inputted TV signal. This circuit employs, for example, a television signal converter.
2. Description of Related Art
As shown in a block diagram of FIG. 1, a typical TV system converter 1 is equipped with a TV system discriminator 2 for automatically discriminating a TV system (for example, the NTSC system or the PAL system) corresponding to a TV signal inputted at an input stage.
When the television system discriminated by the TV system discriminator 2 coincides with the television system according to a signal to be outputted from the TV system converter 1 the TV system converter 1, does not change the designation of television system. When the discriminated television system differs from the television system to be outputted from the TV system converter 1, the TV system converter 1 changes over to the television system for the inputted television signal.
Generally, the TV system converter 1 will have a function for converting between two types of television system and the TV system discriminator 2 discriminates as to which of the two types of TV system the inputted TV signal corresponds.
FIG. 2 is a block view showing a related TV system discriminator 2. The TV system discriminator 2 senses whether or not a television signal of a specific television system is inputted. An indication is also given when the TV signal inputted to the TV system discriminator 2 does not correspond to these specific television systems, i.e. when the inputted television signal corresponds to a still further television system different from the two types of television-system.
In FIG. 2, a television input signal 21 such as, for example, a composite television signal or a luminance signal after Y/C separation is inputted to a sync separator 22. A composite synchronized signal is then separated from the television input signal 21 by the sync separator 22 and inputted to the H/V separator 23.
This H/V separator 23 separates a horizontal sync signal (hereinafter referred to as xe2x80x9cH-syncxe2x80x9d) and a vertical sync signal (hereinafter referred to as xe2x80x9cV-syncxe2x80x9d) from the inputted synchronized signal. Here, H-sync is supplied to a field counter 24 and V-sync is supplied to a decoder 25.
The field counter 24 counts the number of V-sync signals that arrive after reset.
The decoder 25 senses the time when the count value of the field counter 24 becomes a line number for one field corresponding to the prescribed TV system. The decoder 25 then detects whether or not this timing is within one horizontal scanning period (gate period) from the timing of V-sync supplied from the H/V separator 23. The decoder 25 then resets the field counter 24 after one horizontal scanning period from the V-sync timing provided by the H/V separator 23.
When the decoder 25 detects that a signal xe2x80x9cfalls within a gate periodxe2x80x9d, the TV input signal is determined to correspond to a prescribed TV system and a sense signal is outputted to the hysteresis circuit 26.
In order to prevent erroneous determinations, the hysteresis circuit 26 finally forms a discrimination signal 27 when the sense signal from the decoder 25 is consecutively inputted prescribed number of times.
As becomes clear from the above description, the TV system discriminator 2 shown in FIG. 2 determines the television system based on the number of lines per one field being different in each television system.
However, there is the fear that it will be difficult for the aforementioned television system discrimination circuit to make discriminations or that the precision of such discriminations will be extremely low when the difference between the line number and field number is small as between two types of TV systems taken as objects of discrimination.
For example, two types of television system exist for TV signals (hereinafter taken as HDTV signals) used in xe2x80x9cHigh Definition Televisionxe2x80x9d (usually referred to as xe2x80x9cHi-Visionxe2x80x9d) where the line number/number of fields per second (field fiequency) are 1125 lines/60 Hz and 1125/59.94 Hz, respectively. In both cases the difference in the number of fields per second is extremely small and discrimination is therefore difficult using the TV system discriminator 2 shown in FIG. 2.
With regards to discrimination between these two types of HDTV signals, a method of discriminating the difference of the sampling frequencies at the time of putting the HDTV signals into digital form based on phase-synchronized locking and unlocking occurring at a horizontal sync signal-referenced PLL circuit has been put forward.
However, this discrimination method employing this PLL circuit cannot be applied to cases where the TV input signal is already in the form of a digital signal.
It is therefore wished to obtain a TV system discriminator that can be applied when a TV input signal is an analog signal or digital signal and that is capable of accurately discriminating between television systems where the difference between the line number and the field number is small.
It is therefore the object of the present invention to provide a television system discriminator that can be applied when a TV input signal is an analog signal or a digital signal and that is capable of accurately discriminating between television systems where the difference between the line number and the field number is small.
In order to achieve the above object, the TV system discriminator of the present invention comprises a separator for extracting a synchronized signal for a TV signal inputted in accordance with one of a plurality of TV systems, a phase difference sensor for sensing a phase difference of this separated synchronized signal and a prescribed reference signal, and a phase difference displacement discriminator for discriminating a TV system corresponding to an inputted TV signal based on the direction of temporal displacement of this phase difference.